An accurate water distribution device outside the tube of falling film surface evaporation tube bundle
By employing a precise water distribution system in the evaporative air cooler, including a water distribution trough, a water guide trough, a water collection trough, and a water guide pipe, the problems of uneven water distribution and ineffective evaporation in surface evaporative air coolers are solved, thereby improving heat transfer intensity and reducing energy consumption and equipment costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHANGHAI LANBIN PETROCHEM EQUIP CO LTD
- Filing Date
- 2023-05-31
- Publication Date
- 2026-07-14
AI Technical Summary
Existing surface evaporative air coolers using the spray water distribution method suffer from problems such as uneven water distribution outside the tubes, large ineffective evaporation, high air flow resistance, and high water loss, resulting in low heat transfer intensity, high equipment investment, and large footprint.
The external precision water distribution system using falling film surface evaporation tube bundles achieves accurate water distribution to the heat exchange tubes by setting water distribution troughs, water guide troughs, water collection troughs, and water guide pipes on the evaporation tube bundles. It utilizes gravity and surface tension to control the uniform distribution of the water film, reducing ineffective evaporation and water loss.
It improves the heat transfer intensity of the evaporative air cooler, reduces air flow resistance and the power consumption of water pumps and fans, reduces equipment investment and floor space, and enhances the technical and economic efficiency of the equipment.
Smart Images
Figure CN116481372B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to technologies for enhancing heat transfer and saving energy and water resources in the field of heat exchange technology. In particular, it relates to surface evaporative air cooling applications that enhance heat transfer on the outer surface of tubes by water evaporation to cool the fluid inside the condenser tubes, thereby reducing water and energy consumption, lowering equipment investment, and saving floor space. Background Technology
[0002] In process industries such as oil refining, chemical engineering, power generation, metallurgy, and light industry, most production processes require cooling fluids after physicochemical processes to bring them close to ambient temperature. High-temperature heat is generally recovered and utilized through heat exchange, while low-temperature heat recovery and utilization is costly, low-value, and difficult; therefore, it is usually released into the atmosphere through cooling. Fluid cooling primarily involves water cooling and air cooling. Water coolers are widely used in process equipment due to their compact structure and economic efficiency. However, air coolers require a large heat exchange area and a large footprint, making air cooling investments significantly higher than water coolers. Furthermore, the heat absorbed by the fluid in a water cooler is still released into the atmosphere after cooling the circulating water. Moreover, water resources are geographically limited, while air is ubiquitous; especially in resource-rich areas where water resources are often scarce, air coolers become the only viable option for fluid cooling. The process industry has a particular need for air-cooled equipment that requires less investment and space. In the 1990s, China researched and developed a technical route that combines water cooling and air cooling, and developed a surface evaporation air cooler. The surface evaporation air cooler takes advantage of the high latent heat of water vaporization and the strong heat exchange capacity of water evaporation. It uses the effect of water evaporation to absorb heat and reduce the temperature of air and water. In low-temperature condensation cooling applications with large processing volume and high heat load, the cooling equipment has low investment and small footprint, and its comprehensive technical and economic advantages are obvious.
[0003] The thermodynamic factors for enhancing heat transfer in surface evaporative air-cooled tube bundles include heat transfer temperature difference, vacuum level, and relative humidity. In engineering applications, when the fluid temperature is above 80℃, dry air cooling is considered technically and economically comparable; when the fluid temperature is below 60℃, wet air cooling and evaporative air cooling are considered to have greater technical and economic advantages. Increased vacuum level is beneficial for the evaporation of liquid outside the tubes; however, excessively high vacuum levels increase fan power consumption and ineffective water dissipation. Based on the relative humidity of the air at the location and time of the air-cooled equipment, the dry-bulb and wet-bulb temperature difference can be utilized to humidify and cool the air, increasing the heat transfer temperature dynamics and specific heat capacity, thereby reducing the heat exchange area of the air cooler. Existing surface evaporative air cooling uses a water distribution method of uniformly spraying water across the entire windward cross-section of the tube bundle; given the large number of tube rows in the evaporative tube bundle, increasing the water spray volume is mainly used to ensure uniform water distribution and even coverage of the tube walls at the rear of the tube bundle; another method is to divide the tube bundle into multiple groups and add water spray facilities between each group of tube rows. This water spraying method is simple in structure and low in cost; however, in order to improve the uniformity of water distribution on the outer wall of the heat exchange tubes and form a film flow, the spray volume is several times or even tens of times the evaporation volume. This brings a series of side effects. First, the increased spray volume increases the thickness of the liquid film outside the tubes. When the liquid film thickness exceeds a certain value, the proportion of sensible heat conduction and heat transfer on the outer wall of the tubes becomes too high, while the proportion of evaporation heat transfer on the surface of the liquid film decreases. Overall, the heat transfer intensity outside the tubes is lower than the evaporation intensity of ideal film evaporation. Second, the channels between the tubes in the tube bundle heat exchange are air channels, and the projected area of the heat exchange tubes accounts for about half of the total windward area. Water is sprayed on the windward surface corresponding to the channels between the tubes. After leaving the nozzle, the water becomes fine droplets. These droplets come into contact with the air in the channels between the tubes for mass and heat transfer in both the headwind and headwind directions. In the headwind film distribution mode, the air changes from an unsaturated state to a saturated state before it exchanges heat with the water film on the outer wall of the tubes, weakening the driving force for air to come into contact with the water film on the outer wall of the tubes for evaporation and heat transfer. In the reverse-wind membrane distribution mode, the high-velocity air carries some water droplets upwards ineffectively, drifting out of the air-cooled fan channel, resulting in the dissipation of harmful substances. Furthermore, the contact between air and water in the inter-pipe channel significantly increases airflow resistance, necessitating an increase in fan head. This increase in fan head, however, leads to a substantial increase in ineffective water flow and water loss outside the pipes. To capture this ineffective water and prevent its drift and loss, a water removal system must be added below the fan at the top of the tube bundle, further increasing the fan's power consumption. Moreover, the small throat channels of the surface evaporative air-cooled nozzles and the open-loop spray water circulation system are particularly prone to nozzle clogging. In view of this, this invention proposes an accurate overflow water distribution method. Water distribution troughs, corresponding to each heat exchanger tube, are installed at the top and middle of the horizontally arranged evaporative tube bundle to accurately distribute water to each row of heat exchangers. A re-distribution system—a water guide trough—is installed between adjacent rows of heat exchangers. The water distribution system guides the water from the bottom of the water distribution trough and horizontal heat exchange tubes to flow accurately to the top of the adjacent lower heat exchange tubes.This invention solves the engineering problems of inaccurate and uneven water distribution outside the heat exchange tubes of falling film surface evaporation tube bundles, large ineffective evaporation, large evaporation water circulation volume, and large air flow resistance. Summary of the Invention
[0004] The purpose of this invention is to propose a novel method and facility for accurate external water distribution of falling film surface evaporation tube bundles.
[0005] The technical solution of the present invention is as follows: a precise water distribution device for a falling film surface evaporation tube bundle. For evaporation tube bundles with horizontally arranged heat exchange tubes, a water distribution trough, a water guide trough, a water collection trough, and a water guide pipe are provided. The water distribution trough is located above the heat exchange tubes in the same vertical column, or when there are many heat exchange tubes (the number of tube rows in the evaporation tube bundle is large, and a single water distribution trough will make the liquid film thickness on the heat exchange tubes adjacent to the water distribution trough too thick, and the heat exchange tubes below that are beyond a certain distance may dry out. Dividing the tube bundle into multiple groups of water distribution units will make the water distribution uniformity on the outer wall of each group and each row of heat exchange tubes more similar). The water distribution trough is provided above the evaporation tube bundle in the same vertical column and between the heat exchange tubes (the evaporation tube bundle in the same vertical column is divided into multiple groups of water distribution heat exchange tube units, each group of water distribution heat exchange tube units contains a certain number of tube rows of heat exchange tubes, and a water distribution trough and its shielding trough are provided on its upper part, and a water guide trough is provided between each row of heat exchange tubes in each group). The water distribution trough extends axially along the evaporator tube bundle. The trough is generally U-shaped or oblong, with an open top and several overflow outlets on its long side walls. The bottom center of the trough is concave upwards along its long side, forming a long groove. The bottom bend of the long groove's outer surface forms two guide weirs. The guide trough is positioned between adjacent heat exchange tubes. Its top connects to the liquid sac at the bottom of the upper heat exchange tube, and its lower edge approaches but does not contact the upper wall of the lower heat exchange tube. The guide trough consists of an upper W-shaped water receiving structure and two side plates. The bottom of the side plates is not closed. Several window panels are cut out from the two plates at the middle corner of the water receiving structure. The bottom edge of the window panel is connected to the bottom of the W-shaped water receiving structure, while the top part is not connected to the W-shaped water receiving structure and slopes downward to form a drain outlet for the water flow, so that the water flows downward along the inner wall of the side plate of the water guide trough. A water collection trough is set at the bottom of the bottom row of heat exchange tubes of the evaporator tube bundle. The structure of the water collection trough is different from that of the water guide trough in that the bottom and both ends of the side plates are closed, and at certain intervals in the bottom closed area, water guide pipes are set perpendicular to the center line of the heat exchange tubes. The upper end of the water guide pipe is connected to the inside of the water collection trough, and the lower end is connected to the water collection tank.
[0006] Preferably, the overflow outlet is formed by cutting a trapezoidal plate from the long side wall panel and folding it inward. The folded plate forms a certain angle with the long side wall panel, and the bottom edge of the trapezoidal plate remains connected to the long side wall panel. The intermittent and uniform distribution of the overflow outlets ensures that the water flowing out of the overflow outlets flows in a continuous stream, resulting in a uniform water flow.
[0007] Furthermore, a transverse groove is provided in the middle of the water distribution tank. Water accelerates downwards under gravity, and due to the surface tension effect, it tends to converge during flow. To suppress and resist this convergence effect, an active agent is added to the water, significantly reducing its surface tension. Structurally, the uniform transverse groove inhibits the accelerated downward flow of water, changing its flow direction to allow the water film to diffuse inwards and laterally, uniformly covering the surface of the water distribution tank before flowing downwards.
[0008] Furthermore, a water film diffusion groove is provided on the side plate of the water guiding trough. The water collection trough may or may not be equipped with a water film diffusion groove.
[0009] Furthermore, a shielding groove of the same length as the water distribution tank is installed outside the water distribution tank. This shielding groove completely covers the top and sides of the U-shaped or oblong cross-section water distribution tank, maintaining a certain gap. In cross-section, the top shielding groove is inverted U-shaped, while the middle shielding groove covering the outside of the water distribution tank is thin-plate-like with a bent upper part, and its channel width is greater than the width of the water distribution tank. The top shielding groove is suspended from the heat exchanger box wall, and the middle shielding groove is connected to the top edge of the water distribution tank. The shielding groove completely covers the top and sides of the water distribution tank, maintaining a certain gap to block the mass and heat transfer between the flowing air and the water film outside the water distribution tank. The shielding groove must not impede the film formation and flow on the outer wall of the water distribution tank.
[0010] The beneficial effects of this invention are as follows: This invention solves the engineering problems of inaccurate and uneven water distribution outside the falling film surface evaporation tube bundle heat exchanger, large ineffective evaporation, large evaporation water circulation volume, and high air flow resistance. This technology improves the surface evaporation heat transfer intensity of the air-cooled heat exchanger tubes, reduces ineffective water loss, reduces air flow resistance, and saves power consumption of water pumps and fans. Attached Figure Description
[0011] Figure 1 This invention relates to a heat exchange tube horizontally arranged tube bundle and a heat exchange tube water distribution device. The left figure is an axial side view and the right figure is an axial direction view of the heat exchange tube.
[0012] Figure 2 This is a schematic diagram of the water distribution in the top water distribution trough of the horizontally arranged heat exchange tube bundle; the upper left image shows the shielding trough in the installed state, the upper right image shows the axial direction view of the heat exchange tubes; the lower left image shows the shielding trough in the separated state, and the lower right image shows the axial direction view of the heat exchange tubes.
[0013] Figure 3 This is a schematic diagram of the water guide channel for a horizontally arranged heat exchange tube bundle. The left figure is an axonometric view, and the middle and right figures are cross-sectional views at two different locations.
[0014] Figure 4 This is a schematic diagram of the water distribution trough connecting the horizontally arranged heat exchange tube bundle. The left figure is an axonometric view, the middle figure is a cross-sectional view, and the right figure is a cross-sectional view with a shielding groove.
[0015] Figure 5 This is a schematic diagram of the water collection trough and water guide pipe below the bottom heat exchange tubes of the horizontally arranged heat exchange tube bundle. The left figure is an axonometric view and the right figure is a cross-sectional view.
[0016] In the diagram: 1. Water distribution trough, 2. Water guiding trough, 3. Water collection trough, 4. Water guiding pipe, 5. Heat exchange pipe, 6. Shielding trough, 1-1. Overflow outlet, 1-2. Guide weir, 1-3. Horizontal trough, 2-1. W-shaped water receiving structure, 2-2. Side plate, 2-3. Window plate, 2-4. Water film diffusion trough. Detailed Implementation
[0017] Falling film surface evaporative air cooling is widely used in process industry plants for small-temperature heat exchange applications involving media at near-ambient temperatures. Utilizing the heat absorption effect of water evaporation to cool air and water, it cools the fluid within the condenser tubes, significantly reducing investment in air cooling equipment and its footprint, resulting in good technical and economic efficiency. To improve the evaporative cooling effect of evaporative air-cooled tube bundles, reduce power consumption, and further enhance their technical performance, this invention makes an innovative contribution to reducing equipment investment, conserving water resources, and saving energy consumption in the process industry. It proposes a new accurate overflow water distribution method and its facilities for evaporative tube bundles, replacing the existing comprehensive spray water distribution method.
[0018] Implementation Plan: Accurate Water Distribution Method and Facilities for Horizontally Arranged Heat Exchanger Tube Bundles
[0019] like Figure 1 The diagram shows a water distribution method and facility for a single row of evaporator tube bundles with horizontally arranged heat exchange tubes according to the present invention. Figure 2 This is a schematic diagram of water distribution in a water distribution trough. Figure 3 This is a schematic diagram of a water guide channel. Figure 4 This is a schematic diagram showing the connection between the water guide channel and the water distribution channel. Figure 5This is a schematic diagram of a water collection tank. The evaporative air-cooled tube bundle typically has 8-12 rows of heat exchange tubes, with multiple rows of tubes along the width of the bundle. Along the air-water flow direction, a row of heat exchange tubes is divided into multiple groups, typically with 3-6 rows per group. This ensures that the liquid film thickness on the outer surface of the first and last rows of tubes within a group is not significantly different. The next group of heat exchange tubes receives additional circulating water on top of the remaining water from the previous group. A water distribution trough 1 is installed at the top of each row of heat exchange tubes 5, using gravity overflow to accurately distribute water to the top of each row of heat exchange tubes 5. A water guide trough 2 is installed at the bottom of each row of heat exchange tubes, and a water collection trough 3 and a water guide pipe 4 are installed at the bottom of the bottom heat exchange tubes. The lengths of the water distribution trough 1, water guide trough 2, and water collection trough 3 are equivalent to the effective heat exchange length of the heat exchange tubes 5. The cross-sectional shape of the water distribution trough 1 is U-shaped or oblong, with evenly distributed water overflow windows on both sides of its top, serving as overflow outlets 1-1. The lower edge of the windows is horizontal, and the lower edges of all windows are at the same height. The opening height ensures that the water level will not reach the top edge of the water distribution trough 1 due to surface tension. The total height of the water distribution trough 1 meets the requirements for water level stability. A guide weir 1-2 is provided directly below the water distribution trough 1 to prevent the water flowing down from both sides from merging. The top wall of the adjacent heat exchange tube is located directly below the water distribution trough 1.
[0020] The water guide trough 1 and the water collection trough 2 have side plates 2-2 on both sides, which are equivalent to the effective heat exchange length of the heat exchange tubes. These side plates are used to block the direct contact mass and heat transfer between the water flowing downward between the heat exchange tubes and the air. The width of the side plates 2-2 matches the spacing between the heat exchange tubes. Between the side plates 2-2, there is a W-shaped water receiving structure 2-2 to guide the water in the lower part of the upper heat exchange tube to flow downward. The top of the W-shaped water receiving structure 2-2 is close to the wall of the upper heat exchange tube. The middle of the W-shaped water receiving structure 2-2 is a corner plate, which guides the water flow to both sides and divides it into two streams. The window plate 2-3 on the corner plate is separated from the corner plate except for the bottom edge. The water flows from the drain formed by the window plate 2-3 to the inner wall of the side plate 2-2, and then the water flows downward along the inner wall of the side plate 2-2 to the upper surface of the lower heat exchange tube.
[0021] A water collection trough 3 and a water guide pipe 4 are installed below a row of heat exchange tubes at the bottom of the tube bundle. The structure of the water collection trough 3 is basically the same as that of the water guide trough 2, except that the bottom and ends of the side plates 2-2 on both sides are closed, and at certain intervals in the closed area at the bottom, a water guide pipe 4 is installed perpendicular to the center line of the heat exchange tubes. The upper end of the water guide pipe 4 is connected to the inside of the water collection trough 3, and the lower end is connected to the water collection tank below.
[0022] The flowing water used for evaporation outside the evaporative air-cooled tube bundle consists of two parts: one part is circulating water, used to ensure the formation of a uniform and stable evaporative liquid film on the heat exchange tube wall; the other part is makeup water, used to offset the water consumed during normal evaporation. The circulating evaporation water is pressurized by a pipeline pump and then flows into a network of distributed pipes, and then evenly enters the water distribution tanks of each row and group. In the water distribution tank 1, the water level absorbs the kinetic energy of the water supplied by the pipe network, so that the water level rises steadily and slowly. When the water level reaches or exceeds the lower edge of the overflow port of the water distribution tank 1, the gravity of the water overcomes the surface tension and flows downward from the inside to the outside from the lower edge of the overflow port 1-1. Then, due to the effect of surface tension, the surface area of the water film outside the water distribution tank 1 will be minimized. The water tends to flow in droplets or streams on the metal surface of the water distribution tank 1 and the heat exchange tube 5. This can be achieved by adding surfactants to the water to reduce the surface tension of the water, so that the water spreads thinly and evenly into a film flow after contacting the metal wall, or by increasing the water volume to change the water flow from stream flow to film flow. The water on the outer wall of the water distribution tank 1 continues to flow downwards at an accelerated speed to the guide weir 1-2 at the bottom of the water distribution tank 1. The water on both sides does not merge, but forms two water curtains under the action of gravity. The water curtains are pulled downwards and thinned under the action of gravity. The leading edge of the water curtain reaches both sides of the cross-section of the heat exchange tube below to form a continuous water bridge, so that the water is evenly distributed on both sides of the heat exchange tube, thus completing the water distribution function and achieving the goal of uniform distribution: uniform in length direction and uniform on both sides.
[0023] Utilizing the properties of gravity and surface tension, water flowing from the water distribution tank to the outer wall of the first row of heat exchange tubes flows downwards along the outer wall. In the upper wrap-around region of the heat exchange tube cross-section, the combined force of water film tension and gravity accelerates the flow and thins the liquid film. In the lower wrap-around region, gravity causes the liquid to flow downwards, tending to detach from the wall, while surface tension causes the liquid to wrap around the wall. These two forces combine to form a liquid pocket with a certain wrap-around angle and varying thickness at the bottom of the heat exchange tube; it is thickest at the bottom and gradually thins upwards. The water receiving structure between adjacent rows of heat exchange tubes, located near the outer wall of the upper heat exchange tube, serves to connect the lower liquid pocket of the upper heat exchange tube and guide the liquid from the lower part of the upper heat exchange tube into the water guide tank, thus reducing the wrap-around angle and thinning the liquid film at the bottom of the upper heat exchange tube. The lower edges of the water-receiving structure in the middle of the two side plates of the water guide channel slope to both sides, guiding the water flow to the inner wall of the water guide channel side plates. The water flows downward along the inner wall of the water guide channel, forming two water curtains. The lower edge of the water guide channel approaches the upper wall of the lower heat exchange tube but does not contact it. The lowest part of the water curtain approaches the two sides of the cross-sectional wall of the lower heat exchange tube, forming downward flowing water bridges, so that the liquid is evenly distributed on both sides of the heat exchange tube and does not deviate to one side of the heat exchange tube.
[0024] When the next set of water distribution units is arranged below the lower heat exchange tubes of a row of heat exchange tubes, the aforementioned water distribution flow method is repeated to achieve accurate and uniform distribution of water on the heat exchange tube surface. The water collection tank set at the bottom of the lowest row of heat exchange tubes collects the remaining unevaporated water, and then the water is guided to the water tank below the tube bundle (not shown in the figure) through the water guide pipe connected to its lower part.
[0025] In the cross-section of the heat exchanger tube, the thickness of the liquid spool at the bottom is much greater than the thickness of the liquid film on the upper wall. As the liquid spool grows, it continuously absorbs heat from the fluid inside the tube. The thermal conductivity within the liquid spool is lower than the mass-heat transfer between the outer surface of the spool and the air, making it the main component of the thermal resistance for heat transfer outside the tube. The W-shaped water-receiving structure prevents the liquid spool at the bottom of the heat exchanger tube from forming a completely unobstructed thickness. Reducing the thickness of the liquid spool at the bottom of the heat exchanger tube increases the heat transfer from inside the tube to the liquid film and then to the air, thus improving the heat exchange efficiency.
Claims
1. A precise water distribution system for a falling film surface evaporation tube bundle, characterized in that: For evaporator tube bundles with horizontally arranged heat exchange tubes, a water distribution trough (1), a water guide trough (2), a water collection trough (3), and a water guide pipe (4) are provided. The water distribution trough (1) is located above the heat exchange tubes in the same vertical column, or when there are many heat exchange tubes, it is set above the evaporator tube bundle in the same vertical column and between the heat exchange tubes. The water distribution trough (1) extends along the axial direction of the evaporator tube bundle. The water distribution trough (1) is a U-shaped long trough with an open top. The long side wall is provided with several overflow ports (1-1). The bottom edge of the overflow ports (1-1) is horizontal. The middle position of the bottom of the water distribution trough (1) is concave upward along the long side to form a long groove. The bottom bend of the outer surface of the long groove forms two guide weirs (1-2). The water guide trough (2) is located between adjacent heat exchange tubes (5). The top of the water guide trough (2) is connected to the bottom liquid sac of the upper heat exchange tube, and the lower edge is close to the upper wall of the lower heat exchange tube without contacting it. The trough (2) is composed of an upper W-shaped water receiving structure (2-1) and two side plates (2-2). The bottom of the two side plates (2-2) is not closed. The two plates in the middle of the W-shaped water receiving structure (2-1) have several window plates (2-3). The bottom edge of the window plate (2-3) is connected to the bottom of the W-shaped water receiving structure (2-1), and the upper part is not connected to the W-shaped water receiving structure (2-1) and is inclined downward to form a water outlet for water flow, so that the water flows downward along the inner wall of the side plate (2-2) of the water guide trough (2). A water collection trough (3) is set at the bottom of the bottom row of heat exchange tubes of the evaporation tube bundle. The structure of the water collection trough (3) is different from that of the water guide trough (2) in that the bottom and two ends of the two side plates (2-2) are closed, and at certain intervals in the bottom closed area, a water guide pipe (4) is set perpendicular to the center line of the heat exchange tube. The upper end of the water guide pipe (4) is connected to the inside of the water collection trough (3), and the lower end is connected to the water collection tank.
2. The precise water distribution system outside the falling film surface evaporation tube bundle as described in claim 1, characterized in that: The overflow outlet (1-1) is formed by cutting a trapezoidal plate from the long side wall panel and folding it inward, with the bottom edge of the trapezoidal plate connected to the long side wall panel.
3. The precise water distribution system outside the falling film surface evaporation tube bundle as described in claim 1, characterized in that: The water distribution trough (1) has a horizontal groove (1-3) in the middle.
4. The precise water distribution system outside the falling film surface evaporation tube bundle as described in claim 1, characterized in that: The water guide channel (2) has a water film diffusion channel (2-4) on its side plate (2-2).
5. The precise water distribution system outside the falling film surface evaporation tube bundle as described in claim 1, characterized in that: A shielding groove (6) of the same length as the water distribution trough (1) is set outside the water distribution trough (1). The shielding groove (6) completely covers the top and sides of the U-shaped cross-section water distribution trough (1) and maintains a certain gap. The channel width of the shielding groove (6) is greater than the width of the water distribution trough.